This section provides background information related to the present disclosure, which is not necessarily prior art.
In matchplate sand mold casting, the mold comprises separate open-face cope and drag halves that are fabricated separately, and then joined together, face-to-face prior to pouring the molten metal. Conventionally, the cope and drag molds are formed using a pair of boxes called flasks which are filled with sand with a removable pattern-half embedded in each. When removed, the pattern-halves leave an impression in the sand of the part to be cast. The cope contains the impression of the upper half of the part and the drag contains the impression of the lower half of the part. The cope also typically includes a pouring cup passageway into which molten metal may be poured, and also a vent to allow air to escape during the pour. To ensure a properly molded part is produced, the cope and drag halves must fit together in perfect alignment.
The conventional technique for joining the cope and drag halves involves at least two human workers and a lifting crane. First the cope and drag sand molds are formed in their respective flasks. Then a lifting crane is attached to the cope flask and the structure is lifted and inverted, so that the open-face mold side of the cope is facing downward. Human workers then guide the cope as it is lowered into place on top of the drag. The typical lifting and rotating device is rigidly attached to the outer side walls of the flask by brackets carried on a mechanism journaled for rotation about a horizontal axis. Alignment of cope and drag is accomplished visually and manually. Thus high accuracy in the lifting crane and rotating mechanism is not usually required.
With the advent of chemically bonded, no-bake sand, it is now possible with smaller molds (e.g., flask dimensions of about 48 inches or less) to perform the lifting and rotating operation with the flasks removed from the respective cope and drag portions prior to inversion and installing of the cope onto the drag. As before, human operators visually and manually guide the cope into proper position. The lifting and rotating mechanism is different, however, because it must attach directly to the sand sidewalls of the cope. In this application the side walls of the molds are typically slightly tapered or frustum-shaped, having a taper of approximately two degrees to five degrees to allow the mold to be slidably removed from the flask without dismantling the flask and without damaging the mold.
Due to this slight inward taper of the sand mold, an articulated joint or knuckle, such as a ball joint or universal joint, is required to allow the attachment plate secured to the mold to change its angle with respect to the rotational axis as 180 degree rotation is effected. However, to ensure that the cope and drag will fit together in perfect alignment, the articulated joint must be manufactured with high precision, as any displacement caused by poor tolerance in the joint will throw the rotated mold out of alignment when it is inverted.